For the side incident type light guide plate, in the following, for the sake of description, we will call an area of the light guide plate close to the light incident surface as the near-light area, and the area far from the light incident surface as the far-light area.
If an incident light source of a side incident type light guide plate is sequentially arranged at a side of the light incident surface of the light guide plate along a length direction of the light incident surface of the light guide plate in the form of a plurality of discrete light sources, the brightness of the light emitted from the near-light area is higher than that from the far-light area. For the convenience of description, the brightness difference due to the different distances from the light incident surface is hereinafter referred to as a longitudinal brightness difference.
In addition, in a length direction (transverse direction) of the light incident surface of the light guide plate, the light emitted from the light emitting surface portions aligned with or corresponding to the positions of the light sources is generally bright, and the light emitted from the light emitting surface portions deviated from the positions of the light sources is generally dark. For instance, the light emitted from the portion corresponding to the midpoint between two adjacent light sources is generally the darkest. For the convenience of description, the brightness difference due to the various deviation degree from the light sources in the transverse direction is hereinafter referred to as the transverse brightness difference.
In general, the transverse brightness difference in the near-light area is greater than that in the far-light area. In order to reduce the transverse brightness difference in the near-light area, there is a precedent in the art, in which the aim is achieved by reducing the pitch of the light sources so as to increase the distribution density of the light sources. However, this method increases the number of light sources per unit area, adding extra cost. And this method cannot alleviate the problem of longitudinal brightness difference.